Technical Field
The present invention relates to a boiling-water-type geothermal heat exchanger and boiling-water-type geothermal power generation equipment that are capable of efficiently extracting geothermal energy.
Background Art
Geothermal power generation to generate electric power while utilizing geothermal energy uses a high-temperature magma layer as a heat source, and is able to utilize its energy as semi-permanent thermal energy, and does not produce a greenhouse gas in the process of power generation, and hence has attracted attention as an alternative means to fossil fuel in recent years.
In conventional geothermal power generation, boring is conducted at a geothermal region, and electric power is generated by extracting natural steam and hot water present in the geothermal region while utilizing natural pressure. Therefore, the thus extracted steam and hot water contain a large amount of sulfur and other impurities unique to the geothermal region. The impurities adhere to a thermal well, piping, turbines, etc., as scale. The adhesion of scale thereto decreases the output of power generation with the lapse of time, and makes prolonged use difficult.
In order to solve this problem resulting from scale, a technology that adopts a process of extracting hot water by feeding water from the ground and then heating the water with heat supplied from a geothermal region is disclosed by Patent Document 1.
The technology disclosed by Patent Document 1 is concerned with a method for extracting a high-pressure single phase flow extracted by a geothermal heat exchanger installed underground in the form of steam by use of a water separator disposed on the ground, and has a great advantageous effect in that the problem resulting from scale is solved and, in addition, geothermal energy is effectively usable.
With respect to geothermal exchange, the following possible problems will be further mentioned. First, a problem resides in the fact that the power of a high-pressure pump must be increased because of the pressure loss in piping of water fed under the ground and of hot water extracted by obtaining the supply of geothermal energy and in the fact that the diameter of a geothermal heat exchanger is required to be increased in order to raise generating efficiency while restricting the pump power to a low level.
Second, a problem resides in the fact that although the replacement of existing boreholes can be mentioned as one of the advantages brought about by Patent Document 1, boreholes to which replacement is applied are limited by limitations on the diameter of a geothermal heat exchanger. The size of the diameter of a geothermal heat exchanger might be an obstacle even when the replacement etc., of boreholes for a geothermal energy survey and of boreholes being out of service are investigated, besides the replacement of existing boreholes.
In Patent Document 2, as a problem to be solved so that a unit power generation cost is reduced by raising the energy efficiency of a geothermal power generation system and by restraining an increase in cost of pumps and so forth, a steam generating method for geothermal power generation is described in which a liquid is lowered from the ground to a geothermal region and is allowed to absorb heat at the geothermal region, and the pressure of the liquid that has thus absorbed heat is decreased to reach pressure equal to or less than saturated steam pressure in the process of raising the liquid that has absorbed heat from the geothermal region.